1. FIELD OF THE INVENTION
The present invention relates generally to a compressor for compressing a refrigerant.
More particularly, the present invention relates to a slidable part preferably employable for a rotational speed variable type refrigerant compressor.
Further, the present invention relates to a rotational speed variable type refrigerant compressor having the foregoing slidable part used therefor.
2. DESCRIPTION OF THE RELATED ART
To improve a property of wear resistance of machine parts or components, various kinds of nitriding treatments have been heretofore carried out for the machine parts or components. In addition, it has been found that reliability of an apparatus or device can be improved and its running life can be elongated by utilizing the technology of nitriding treatment.
This technology of nitriding treatment will briefly be described below with reference to a refrigerant compressor as one example. For example, a rotary type refrigerant compressor is constructed such that a motor mechanism and a compressing mechanism are arranged in a closed casing. The motor mechanism is operatively connected to the compressing mechanism via a shaft extending therebetween. The compressing mechanism is driven by the motor mechanism via the shaft.
The shaft extends through a cylinder of the compressing mechanism, and the upper and lower ends of the shaft are rotatably supported by bearings. Specifically, the shaft is rotatably supported by a bearing in the housing and a sub-bearing at the lower end thereof. A part of the shaft in a cylinder is machined in the form of a crank, and a roller is rotatably fitted onto the crank. In addition, a blade extends through the cylinder to divide the interior of the cylinder into a suction chamber and a discharge chamber. One end of the blade comes in slidable contact with the outer surface of the roller by the biasing force of a spring. As the shaft is rotated, the roller repeatedly performs planetary movement, causing a refrigerant to be compressed. The compressed refrigerant is once discharged into the casing and it is then supplied to the refrigerator side via a discharge tube extending from the casing.
As mentioned above, the shaft is rotated while coming in slidable contact with the bearing surfaces of the frame and the subbearing. To smoothly carry out slidable movement of the slidable part, a refrigerator oil is received and stored in the casing. The refrigerator oil is sucked up by a pump disposed at the lower end of the shaft so as to allow respective slidable parts to be lubricated with the refrigerator oil.
As will be apparent from the above description, wear of the shaft and associated components becomes a significant problem. Specifically, a thrust portion on the lower surface of the crank of the shaft is rotatably brought in slidable contact with the subbearing while receiving the dead weight of the shaft in the motor mechanism as well as the dead weight of the rotor in the compressing mechanism. When a film of lubricant on the slidable surface is broken, the slidable contact surface between the upper surface of the subbearing and the lower surface of the crank of the shaft is worn as the shaft is rotated. In addition, since the shaft receives the biasing force of the spring via the roller and moreover receives a pressure in the cylinder, the shaft is thrusted against the frame and the subbearing, whereby the shaft is forcibly rotated in the slightly bent or curved state. For this reason, when the lubricant film is broken, the outer surface of the shaft and the inner surfaces of the frame and the subbearing are worn undesirably. To prevent an occurrence of wearing as mentioned above, endeavors have been made to improve a property of wear resistance, e.g., by allowing the surface of the shaft to be subjected to various kinds of nitriding treatments to form an iron nitride layer on the surface of the shaft.
However, with respect to a refrigerant compressor including a rotational speed variable type motor, there arises a problem that a sufficiently high effect for preventing wear can not be obtained merely by carrying out nitriding treatment, because the shaft is rotated within the wide operational range from a very low rotational speed to a very high rotational speed. Especially, when the shaft is rotated at a low rotational speed lower than 30 Hz, the lubricant film between the shaft and the bearing is easily broken. Once the lubricant film is broken, an opponent member is largely worn, though wear on the shaft side is suppressed considerably. On the contrary, when the shaft is rotated at a high rotational speed in excess of 120 Hz, a malfunction of hot seizure readily takes place even with the shaft which has been subjected to nitriding treatment, because a large magnitude of load is imparted to the shaft. FIG. 7 is a diagram which illustrates that a quantity of wear varies depending on the rotational speed of the shaft.
In view of the foregoing problem, to elevate reliability of the rotational speed variable type refrigerant compressor, many requests have been raised from users so as to improve a property of wear resistance of the slidable members during operation of the refrigerant compressor not only at a very low rotational sped but also at a very high rotational speed, because the lubricant film is easily broken at these rotational speeds.